The present invention relates to a method of and a system for controlling servo activating hydraulic fluid pressure for a motor vehicle automatic transmission.
An automatic transmission of the RE4R03A type is known. This known automatic transmission is described in a publication "NISSAN FULL-RANGE AUTOMATIC TRANSMISSION RE4R03A TYPE, SERVICE MANUAL, (A261C10)" issued on March 1988 by NISSAN MOTOR COMPANY LIMITED. According to this publication, it is known to determine servo activating hydraulic fluid pressure in response to throttle opening degree. A plurality of line pressure tables are stored in a microcomputer based control unit. Each of the line pressure tables contains line pressure values versus various throttle opening degrees. In this control, the throttle opening degree is used to indicate load on the engine. For a 1-2 upshift, for example, a table look-up operation of a line pressure table for 1-2 upshift is performed using a throttle opening degree to determine servo activating hydraulic fluid pressure supplied to engage on-coming friction device. In this case, the throttle opening degree is used to represent a torque before the 1-2 upshift. Thus, the servo activating hydraulic fluid pressure is fixed to a single value determined by throttle opening degree detected before the shift.
This known system for controlling servo activating hydraulic fluid pressure is not satisfactory in that, with the same throttle opening degree, servo activating hydraulic fluid pressure remains invariable even if there occurs a change in driving force.
An object of the present invention is to provide an adaptive correction of servo activating hydraulic fluid pressure in agreement with driving force variability.